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The rapid growth of distributed processing has led to the adoption of the Reference Model of Open Distributed Processing (RM-ODP, ITU-T Rec. X.901-X.904 | ISO/IEC 10746). This Reference Framework is a joint effort by ISO, IEC and ITU-T, which provides a coordinating framework for the standardization of open distributed processing (ODP) which supports distribution, interworking, platform and technology independence, and portability, together with an enterprise architecture framework for the specification of ODP systems.
The RM-ODP family of recommendations and international standards defines essential concepts necessary to specify open distributed processing systems from five prescribed viewpoints and provides a well-developed framework for the structuring of specifications for large-scale, distributed systems.
The RM-ODP is based on precise concepts derived from current distributed processing developments and, as far as possible, on the use of formal description techniques for specification of the architecture.
The framework for system specification provided by the RM-ODP has four fundamental elements:
Object modelling provides a formalization of well-established design practices of abstraction and encapsulation. Abstraction allows the description of system functionality to be separated from details of system implementation. Encapsulation allows the hiding of heterogeneity, the localization of failure, the implementation of security and the hiding of the mechanisms of service provision from the service user.
Most complex system specifications are so extensive that no single individual can fully comprehend all aspects of the specifications. Furthermore, we all have different interests in a given system and different reasons for examining the system's specifications. A business executive will ask different questions of a system make-up than would a system implementer. The concept of RM-ODP viewpoints framework, therefore, is to provide separate viewpoints into the specification of a given complex system. These viewpoints each satisfy an audience with interest in a particular set of aspects of the system. Associated with each viewpoint is a viewpoint language that optimizes the vocabulary and presentation for the audience of that viewpoint.
RM-ODP defines five viewpoints. A viewpoint (on a system) is an abstraction that yields a specification of the whole system related to a particular set of concerns. The five viewpoints defined by RM-ODP have been chosen to be both simple and complete, covering all the domains of architectural design. These five viewpoints are:
For each viewpoint there is an associated viewpoint language which can be used to express a specification of the system from that viewpoint. The object modelling concepts give a common basis for the viewpoint languages and make it possible to identify relationships between the different viewpoint specifications and to assert correspondences between the representations of the system in different viewpoints.
ODP standards define functions and structures to realize distribution transparencies. ODP standards define functions and structures to realize distribution transparencies. Distribution transparencies enable complexities associated with system distribution to be hidden from applications where they are irrelevant to their purpose. For example:
However, there are performance and cost tradeoffs associated with each transparency and only selected transparencies will be relevant in many cases. Thus, a conforming ODP system must implement those transparencies that it supports in accordance with the relevant standards, but it is not required to support all transparencies.
The RM-ODP also provides a framework for assessing system conformance. The basic characteristics of heterogeneity and evolution imply that different parts of a distributed system can be purchased separately, from different vendors. It is therefore very important that the behaviours of the different parts of a system are clearly defined, and that it is possible to assign responsibility for any failure to meet the system's specifications. The framework defined to govern the assessment of conformance addresses these issues.
RM-ODP consists of four basic ITU-T Recommendations and ISO/IEC International Standards:
In addition, a standard defines use of the UML 2 for expressing the specifications of open distributed systems in terms of the viewpoint specifications defined by the RM-ODP:
This standard (usually referred to as UML4ODP) defines a set of UML Profiles, one for each viewpoint language and one to express the correspondences between viewpoints, and an approach for structuring them according to the RM-ODP principles. The purpose of UML4ODP is to allow ODP modelers to use the UML notation for expressing their ODP specifications in a standard graphical way; to allow UML modelers to use the RM-ODP concepts and mechanisms to structure their large UML system specifications; and to allow UML tools to be used to process viewpoint specifications--thus facilitating the software design process and the enterprise architecture specification of large software systems. Read more about the UML4ODP standard.
Another standard of interest specifies the Enterprise Language:
This standard defines the concepts and structuring rules of an enterprise viewpoint specification, and the possible correspondences with other viewpoints. Read more about the Enterprise Language standard
In the same series as the RM-ODP are a number of other standards and recommendations for the specification and development of open and distributed system, for which RM-ODP provides an standardization framework:
Copies of the RM-ODP family of standards can be obtained either from ISO or from ITU-T. In particular, Parts 1 to 4 of the RM-ODP are available for free download from ISO. Most ODP-related ITU-T Recommendations, including X.9xx series, are also freely available from the ITU-T.
For the MagicDraw
UML tool (used for the standard development):
For other UML tools:
For non-UML users: